Cyanobacteria algae, mosses, liverworts, hornworts and other bryophytes are found growing in, on or adjacent to lawns, gardens, trees, shrubs, golf courses, rooftops, decks and concrete structures. They are non-parasitic, primitive green plants that have fine branched, threadlike stems with tiny leaves. The conditions that favor cyanobacteria algae, moss, liverwort, hornwort and other byrophyte growth include: excessive shade, high levels of moisture, acidic soil, compacted soil, low soil fertility or some combination of these conditions. Mosses typically form a thick, green mat on soil, roof, deck or concrete surfaces. Cyanobacteria algae can grow in similar ways. This growth impedes the surface's use or appearance and can also cause structural damage. Liverworts are similar in appearance to mosses and are often mistaken for moss. Physical removal, chemical treatment or combinations of both are generally used to achieve unwanted cyanobacteria algae, moss, liverwort, hornwort and other bryophyte control.
Physical removal is obviously time consuming, tedious and does not always result in the permanent removal of the unwanted cyanobacteria algae, mosses, liverworts, hornworts and other bryophytes.
Chemical treatment of unwanted cyanobacteria algae, mosses, liverworts, hornworts and other bryophytes requires the application of a chemical, i.e., a herbicide, to the area where the cyanobacteria algae, moss, liverwort, hornwort or other bryophyte is located. Herbicides known for use in control of these plants are heavy metal salts such as ferrous sulfate, ammonium sulfate, ferric ammonium sulfate and copper sulfate. There are considerable shortcomings in using the aforementioned herbicides. For example, these herbicides require very high use rates that can cause phytotoxicity to turf grasses and other plants in runoff conditions. High use rates also result in an accumulation of heavy metals in the soil and surrounding environment.
Clearly, chemical methods of treatment are lacking in some respects for the control of cyanobacteria algae, mosses, liverworts, hornworts and other byrophytes with the herbicides presently being used.
A newer class of herbicides different than those set forth above controls plants by disrupting certain functions in the plant cell. These herbicides are known as inhibitors of the enzyme protoporphyrinogen oxidase (commonly known as PPO-inhibitors), which cause disruption of cell membranes by inducing lipid peroxidation resulting in death to the plant. An example of an herbicidal PPO-inhibitor is carfentrazone-ethyl:

Carfentrazone-ethyl, namely ethyl α,2-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]-4-fluorobenzenepropanoate, is disclosed and claimed in U.S. Pat. No. 5,125,958.